The status of the complement (C) system in gingival crevice fluid (GCF) from individuals with and without periodontal disease will be studied. Main emphasis will be on C3 and C5, two key components in C mediated inflammation. C3 and C5 and their possible cleavage products generated in GCF will be compared and contrasted with highly purified C3 and C5 and their biologically active cleavage products generated under carefully controlled conditions. A detailed physical-chemical analysis will be performed by gel filtration, sucrose density gradient, zone ultracentrifugation and by various modifications of the electrophoretic procedure. The analysis will be aided by the use of radioactively (125I) trace-labelled C proteins, which also will be assayed immunochemically. Powerful monospecific antisera against precursor C3 and C5 fragments and isolated subunits are at our disposal. The functional analysis include tests for hemolytic, chemotactic and anaphylatoxic activities. It is hoped that this study will provide detailed information on the nature of C in GCF from which the degree of C involvement in peridontal disease can be evaluated. Such information may be important not only for the understanding of the pathogenetic mechanisms in peridontal disease but also for human inflammatory disorders in general.